Carbon nanotube array and method for making same

ABSTRACT

A carbon nanotube array is provided. The carbon nanotube array includes at least two isotope-doped carbon nanotube sub-arrays. Each isotope-doped carbon nanotube sub-array includes a plurality of carbon nanotubes. The carbon nanotubes in different isotope-doped carbon nanotube sub-array are composed of different kinds of carbon isotopes. The present disclosure also provides a method for making the carbon nanotube arrays.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201010294641.4, filed on Sep. 28, 2010 inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference. This application is related to anapplications with Ser. No. 13/071,524, entitled, “METHOD FOR MAKINGCARBON NANOTUBE ARRAY”, filed on Mar. 25, 2011.

BACKGROUND

1. Technical Field

The present disclosure relates to a carbon nanotube array and methodsfor making the carbon nanotube array, and particularly to anisotope-doped carbon nanotube array and methods for making theisotope-doped carbon nanotube array.

2. Discussion of Related Art

Isotope labeling is a powerful tool in the study of nano-material growthmechanisms and in nano-sized isotope junction synthesis. Methods ofisotope labeling use reactants containing different isotopes of aspecial element (usually light elements such as carbon, boron, nitrogen,and oxygen), which are fed in designated concentrations (pure or mixed)and sequences into a nano-material synthesis process to provide in situisotope labeling of nano-materials.

A typical example is shown and discussed in U.S. Pat. No. 7,029,751B2,entitled, “ISOTOPE-DOPED CARBON NANOTUBE AND METHOD AND APPARATUS FORFORMING THE SAME,” issued to Fan, et al. on Apr. 18, 2006. This patentdiscloses an isotope-doped carbon nanotube array and method for makingthe same. The isotope-doped carbon nanotube array includes a pluralityof identical isotope-doped carbon nanotubes which are used for labeling.However, the number of labels is limited by a single kind ofisotope-doped carbon nanotubes in the isotope-doped carbon nanotubearray, which limits isotopic labeling.

What is needed, therefore, is to provide a carbon nanotube array whichincludes a plurality of isotope-doped carbon nanotube sub-arrays, and amethod for making the same, to overcome the above-describedshortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 shows a schematic view of one embodiment of a carbon nanotubearray.

FIG. 2 shows a flow chart of one embodiment of a method to form thecarbon nanotube array of FIG. 1.

FIG. 3 shows a schematic diagram of one embodiment of an apparatus usedto form the carbon nanotube array of FIG. 1.

FIG. 4 shows a schematic diagram of one embodiment of introducing thecarbon source gases into the apparatus of FIG. 3.

FIG. 5 shows a schematic view of one embodiment of a carbon nanotubearray.

FIG. 6 shows a schematic diagram of one embodiment of an apparatus usedto form the carbon nanotube array of FIG. 5.

FIG. 7 shows a schematic diagram of one embodiment of introducing thecarbon source gases into the apparatus of FIG. 6.

FIG. 8 shows one embodiment of a carbon nanotube array.

FIG. 9 shows a flow chart of one embodiment of a method to form thecarbon nanotube array of FIG. 8.

FIG. 10 shows a schematic diagram of one embodiment of an apparatus usedto form the carbon nanotube array of FIG. 8.

FIG. 11 shows one embodiment of a carbon nanotube array.

FIG. 12 shows a schematic diagram of one embodiment of an apparatus usedto form the carbon nanotube array of FIG. 11.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1, a carbon nanotube array 10 is disclosed. The carbonnanotube array 10 can be formed on a catalyst layer 130 of a substrate132. The carbon nanotube array 10 is an isotope-doped carbon nanotubearray having a plurality of isotope-doped carbon nanotubes. Eachisotope-doped carbon nanotube includes a first carbon nanotube segment12 and a second carbon nanotube segment 14. The second carbon nanotubesegment 14 is formed on the catalyst layer 130 of the substrate 132. Thefirst carbon nanotube segment 12 is formed on the top of the secondcarbon nanotube segment 14. The first carbon nanotube segments 12 canconsist essentially of carbon-12 isotope. The second carbon nanotubesegments 14 can consist essentially of carbon-12 isotope and carbon-13isotope. The carbon-12 isotope and carbon-13 isotope in the secondcarbon nanotube segment 14 are mixed uniformly in any proportion.Alternatively, the first carbon nanotube segment 12 can consistessentially of carbon-12 isotope and carbon-13 isotope, and the secondcarbon nanotube segment 14 can consist essentially of carbon-12 isotope.

The isotope-doped carbon nanotubes in the carbon nanotube array 10 canbe single-walled carbon nanotubes, double-walled carbon nanotubes,multi-walled carbon nanotubes, or combinations thereof. A diameter ofthe isotope-doped carbon nanotubes can be in a range from about 0.5nanometers to about 50 nanometers. A height of the isotope-doped carbonnanotubes can be in a range from about 50 nanometers to about 5millimeters. The first carbon nanotube segments 12 and the second carbonnanotube segments 14 can have a substantially same height.

Referring to FIG. 2 and FIG. 3, the carbon nanotube array 10 can be madeby the following steps:

(S10) providing a substrate 132 with a catalyst layer 130 on a surfaceof the substrate 132, and placing the substrate 132 into a reactiondevice 100;

(S11) supplying at least two kinds of carbon source gases, each of thecarbon source gases including different kinds of single carbon isotope;

(S12) introducing the at least two kinds of carbon source gases into thereaction device 100 simultaneously; and

(S13) reacting the at least two kinds of carbon source gases underdifferent temperatures to grow the carbon nanotube array 10 on a surfaceof the catalyst layer 130.

In step (S10), the substrate 132 is a polished silicon sheet. Asmoothness of the surface of the substrate 132 is less than 10nanometers. Alternatively, the substrate 132 can also be a polishedsilicon dioxide sheet or a polished quartz sheet.

The catalyst layer 130 can be an iron film. The thickness of the ironfilm can be in a range from about 3 nanometers to about 6 nanometers.The iron film can be uniformly disposed on the surface of the substrate132 by means of chemical vapor deposition, thermal deposition,electron-beam deposition, or sputtering. The material of the catalystlayer 130 can also be a transition metal such as copper, cobalt, nickel,or any alloy thereof.

The reaction device 100 includes a reaction chamber 120, a reactionfurnace 122 for heating the reaction chamber 120, a protective gassupply conduit 102, three carbon source gas supply pipes 104, 106, 108,and a vent-pipe 110. The protective gas supply conduit 102 is controlledby a valve 112. The carbon source gas supply pipe 104 is controlled by avalve 114. The carbon source gas supply pipe 106 is controlled by avalve 116. The carbon source gas supply pipe 108 is controlled by avalve 118.

The substrate 132 with the catalyst layer 130 is placed into thereaction chamber 120. When the substrate 132 is placed into the reactionchamber 120, an angle between the catalyst layer 130 and the horizontaldirection will be formed. In one embodiment, the angle is about 0degrees. In addition, the catalyst layer 130 in the reaction chamber 120can be heated to a predetermined temperature by the reaction furnace122.

In step (S11), the at least two kinds of carbon source gases can besupplied by the three carbon source gas supply pipes 104, 106, and 108.The at least two kinds of carbon source gases can be methane, acetylene,ethylene, allene, or other hydrocarbons. Each kind of carbon source gasincludes a single kind of carbon isotope, for example, carbon-12isotope, carbon-13 isotope, or carbon-14 isotope. In one embodiment, theat least two kinds of carbon source gases are the acetylene including asingle carbon-12 isotope and the ethylene including a single carbon-13isotope.

Step (S12) includes the steps of:

(S121), evacuating the reaction chamber 120 by the vent-pipe 110;

(S122), introducing a protective gas under a pressure of 1 atmosphereinto the reaction chamber 120 through the protective gas supply conduit112; and

(S123), introducing the at least two kinds of carbon source gases intothe reaction chamber 120 simultaneously.

The protective gas can be argon, nitrogen, helium, or neon. After theprotective gas is introduced into the reaction chamber 120, theacetylene including a single carbon-12 isotope and the ethyleneincluding a single carbon-13 isotope are introduced into the reactionchamber 120 simultaneously. The acetylene is introduced into thereaction chamber 120 through the carbon source gas supply pipe 114 at aflow rate of about 120 standard cubic centimeters per minute (sccm). Theethylene is introduced into the reaction chamber 120 through the carbonsource gas supply pipe 116 at a flow rate of about 120 sccm.

In step (S13), the reaction chamber 120 and the catalyst layer 130therein are heated to a first temperature via a heating device (notshown) in the reaction furnace 122. The first temperature can be in arange from about 600° C. to about 650° C. Because the first temperatureonly reaches the decomposition temperature of acetylene but does notreach the decomposition temperature of ethylene, the acetylene includinga single carbon-12 isotope will decompose individually, to grow thefirst carbon nanotube segment 12 having carbon-12 isotope on the surfaceof the catalyst layer 130. After a first given time for growing thefirst carbon nanotube segment 12, the reaction chamber 120 and thecatalyst layer 130 therein are heated to a second temperature by theheating device in the reaction furnace 122. The second temperature canbe in a range from about 650° C. to about 800° C. Because the growthpoints of the carbon nanotubes are at the catalyst layer 130 and thesecond temperature reaches the decomposition temperature of bothacetylene and ethylene, the acetylene and ethylene will decomposesimultaneously, to continuously grow the second carbon nanotube segment14 having carbon-12 isotope and carbon-13 isotope at the bottom of thefirst carbon nanotube segment 12. The carbon-12 isotope and carbon-13isotope in the second carbon nanotube segments 14 are mixed uniformly inany proportion. After a second given time for growing the second carbonnanotube segment 14, the carbon nanotube array 10 is formed on thesurface of the catalyst layer 130.

Alternatively, in step (S13), the reaction chamber 120 and the catalystlayer 130 therein can be first heated to a first temperature in a rangefrom about 650° C. to about 800° C. Because the first temperaturereaches the decomposition temperature of acetylene and ethylene, theacetylene and ethylene will decompose simultaneously, to grow the firstcarbon nanotube segment 12 having carbon-12 isotope and carbon-13isotope on the surface of the catalyst layer 130. After a first giventime for growing the first carbon nanotube segment 12, the reactionchamber 120 and the catalyst layer 130 therein can be cooled down to asecond temperature in a range from about 600° C. to about 650° C.Because the second temperature only reaches the decompositiontemperature of acetylene, the acetylene will decompose individually, togrow the second carbon nanotube segment 14 having carbon-12 isotope atthe bottom of the first carbon nanotube segment 12. Furthermore, theabove steps can be repeated to grow first carbon nanotube segments 12and second carbon nanotube segments 14 alternately arranged along thelongitudinal direction of isotope-doped carbon nanotube.

Referring to FIG. 3 and FIG. 4, in another embodiment, the carbonnanotube array 10 can be made by the following steps:

(S10 a) providing a substrate 132 with a catalyst layer 130 on a surfaceof the substrate 132, and placing the substrate 132 into a reactiondevice 100;

(S11 a) controlling the reaction device 100 at a reaction temperature;

(S12 a) introducing a first carbon source gas into the reaction device100 to grow a first carbon nanotube segment 12, wherein the first carbonsource gas includes a single carbon isotope; and

(S13 a) introducing a second carbon source gas with the first carbonsource gas into the reaction device 100 to grow a second carbon nanotubesegment 14 at the bottom of the first carbon nanotube segment 12,wherein the second carbon source gas includes a single carbon isotopedifferent from the carbon isotope of the first carbon source gas.

In step (S11 a), the reaction temperature can be in a range from about650° C. to about 800° C.

In step (S12 a) and (S13 a), the first carbon source gas is acetyleneincluding a single carbon-12 isotope, and the second carbon source gasis ethylene including a single carbon-13 isotope.

Referring to FIG. 5, a carbon nanotube array 20 is disclosed. The carbonnanotube array 20 can be formed on a catalyst layer 130 of the substrate132. The carbon nanotube array 20 is an isotope-doped carbon nanotubearray having a plurality of isotope-doped carbon nanotubes. Theisotope-doped carbon nanotubes include a first carbon nanotube segment22, a second carbon nanotube segment 24, and a third carbon nanotubesegment 26. The third carbon nanotube segment 26 is formed on thecatalyst layer 130 of the substrate 132. The second carbon nanotubesegment 24 is formed on the top of third carbon nanotube segment 26. Thefirst carbon nanotube segment 22 is formed on the top of second carbonnanotube segment 24. The first carbon nanotube segments 22 can consistessentially of carbon-12 isotopes. The second carbon nanotube segments24 can consist essentially of carbon-12 isotope and carbon-13 isotopes.The third carbon nanotube segments 26 can consist essentially ofcarbon-12 isotopes, carbon-13 isotopes, and carbon-14 isotopes. Thecarbon-12 isotopes and carbon-13 isotopes in the second carbon nanotubesegments 24 are mixed uniformly in any proportion. The carbon-12isotopes, carbon-13 isotopes, and carbon-14 isotopes in the third carbonnanotube segments 26 are also mixed uniformly in any proportion.

Referring to FIG. 6, the carbon nanotube array 20 can be made by thefollowing steps:

(S20) providing a substrate 132 with a catalyst layer 130 on a surfaceof the substrate 132, and placing the substrate 132 into a reactiondevice 100;

(S21) supplying three kinds of carbon source gases, each of the carbonsource gases including different kinds of single carbon isotope;

(S22) introducing the three kinds of carbon source gases into thereaction device 100 simultaneously; and

(S23) reacting the three kinds of carbon source gases react underdifferent temperatures, to grow the carbon nanotube array 20 on asurface of the catalyst layer 130.

In step (20), the reaction device 100 includes a reaction chamber 120,and a laser heating device 140 for heating the reaction chamber 120 andthe catalyst layer 130 therein.

The step (S21) and step (S22) are substantially the same as the step(S11) and step (S 12), the difference is that the carbon source gasesinclude three kinds of carbon source gases. The three kinds of carbonsource gases are methane, acetylene, and ethylene. The methane includesa single carbon-14 isotope, the ethylene includes a single carbon-13isotope, and the acetylene includes a single carbon-12 isotope. Thethree kinds of carbon source gases are introduced into the reactionchamber 120 simultaneously, and the methane is introduced into thereaction chamber 120 through the carbon source gas supply pipe 118 at aflow rate of about 120 sccm.

In step (S23), the reaction chamber 120 and the catalyst layer 130 areheated to a first temperature by the laser heating device 140. The firsttemperature can be in a range from about 600° C. to about 650° C.Because the first temperature only reaches the decomposition temperatureof acetylene but does not reach the decomposition temperature ofethylene and methane, the acetylene including a single carbon-12 isotopewill decompose individually, thus the first carbon nanotube segment 22having carbon-12 isotope will form on the surface of the catalyst layer130. After a first given time for growing the first carbon nanotubesegment 22, the reaction chamber 120 and the catalyst layer 130 areheated to a second temperature in a range from about 650° C. to about800° C. Because the second temperature reaches the decompositiontemperature of acetylene and ethylene but does not reach thedecomposition temperature of methane, the acetylene and ethylene willdecompose together, thus the second carbon nanotube segment 24 havingcarbon-12 isotope and carbon-13 isotope will form at the bottom of thefirst carbon nanotube segment 22. After a second given time for growingthe second carbon nanotube segment 24, the reaction chamber 120 and thecatalyst layer 130 are heated to a third temperature in a range fromabout 850° C. to about 1100° C. Because the third temperature reachesthe decomposition temperature of acetylene, ethylene, and methane, theacetylene, ethylene, and methane will decompose together, thus the thirdcarbon nanotube segment 26 having carbon-12 isotope, carbon-13 isotope,and carbon-13 isotope will form at the bottom of the second carbonnanotube segment 24. After a third given time for growing the thirdcarbon nanotube segment 26, the carbon nanotube array 20 is formed onthe surface of the catalyst layer 130. Furthermore, the above steps canbe repeated to grow the first, second, and third carbon nanotube segment22, 24, and 26 alternately arranged along the longitudinal direction ofthe isotope-doped carbon nanotube.

Alternatively, in step (S23), the temperature of the reaction chamber120 and the catalyst layer 130 therein can be controlled by the laserheating device 140 to achieve different temperatures successively, andthen growing different kinds of carbon nanotube arrays.

Referring to FIG. 6 and FIG.7, in another embodiment, the carbonnanotube array 20 of FIG. 5 can be made by the following steps:

(S20 a) providing a substrate 132 with a catalyst layer 130 on a surfaceof the substrate 132, and placing the substrate 132 into a reactiondevice 100;

(S21 a) controlling the reaction device 100 to a reaction temperature;

(S22 a) introducing a first carbon source gas into the reaction device100 to grow a first carbon nanotube segment 22, wherein the first carbonsource gas includes a single carbon isotope;

(S23 a) keeping introducing the first carbon source gas and introducinga second carbon source gas into the reaction device 100 to grow a secondcarbon nanotube segment 24 at the bottom of the first carbon nanotubesegment 22, wherein the second carbon source gas includes a singlecarbon isotope different from the carbon isotope of the first carbonsource gas; and

(S24 a) keeping introducing the first carbon source gas and the secondcarbon source gas, and further introducing a third carbon source gasinto the reaction device 100 to grow a third carbon nanotube segment 26at the bottom of the second carbon nanotube segment 24, wherein thethird carbon source gas includes a single carbon isotope different fromthe carbon isotope of the first carbon source gas and the second carbonsource gas.

In step (S21 a), the reaction temperature can be in a range from about850° C. to about 1100° C.

In step (22 a), (S23 a) and (S24 a), the first carbon source gas isacetylene including a single carbon-12 isotope, the second carbon sourcegas is ethylene including a single carbon-13 isotope, and the thirdcarbon source gas is methane including a single carbon-14 isotope.

Referring to FIG. 8, a carbon nanotube array 30 is disclosed. The carbonnanotube array 30 can be formed on a catalyst layer 230 of the substrate232. The carbon nanotube array 30 is an isotope-doped carbon nanotubearray including a first isotope-doped carbon nanotube sub-array 32, asecond isotope-doped carbon nanotube sub-array 34, and a thirdisotope-doped carbon nanotube sub-array 36. Each isotope-doped carbonnanotube sub-array includes a plurality of carbon nanotubes. Each carbonnanotube in each isotope-doped carbon nanotube sub-array is made up of asingle carbon nanotube segment. The carbon nanotubes in the firstisotope-doped carbon nanotube sub-array 32 are composed of carbon-12isotope. The carbon nanotubes in the second isotope-doped carbonnanotube sub-array 34 are composed of carbon-12 isotope and carbon-13isotope. The carbon nanotubes in the third isotope-doped carbon nanotubesub-array 36 are composed of carbon-12 isotope, carbon-13 isotope, andcarbon-14 isotope. The carbon-12 isotope and carbon-13 isotope in thecarbon nanotubes of second isotope-doped carbon nanotube sub-array 34are mixed uniformly in any proportion. The carbon-12 isotope, carbon-13isotope, and carbon-14 isotope in the carbon nanotubes of thirdisotope-doped carbon nanotube sub-array 36 are also mixed uniformly inany proportion.

The second isotope-doped carbon nanotube sub-array 34 and thirdisotope-doped carbon nanotube sub-array 36 can have the same shape andsize. In one embodiment, the shape of each of the second and thirdisotope-doped carbon nanotube sub-arrays 34 and 36 is rectangular. Thesecond isotope-doped carbon nanotube sub-array 34 and the thirdisotope-doped carbon nanotube sub-array 36 are formed on the surface ofthe substrate, and spaced from each other. Both of the secondisotope-doped carbon nanotube sub-array 34 and the third isotope-dopedcarbon nanotube sub-array 36 are surrounded by the first isotope-dopedcarbon nanotube sub-array 32. Alternatively, the shape and size of thesecond isotope-doped carbon nanotube sub-array 34 and the thirdisotope-doped carbon nanotube sub-array 36 can be controlled accordingto actual demand.

The carbon nanotubes in the carbon nanotube array 30 can besingle-walled carbon nanotubes, double-walled carbon nanotubes,multi-walled carbon nanotubes, or combinations thereof. The diameter ofthe carbon nanotubes can be in a range from about 0.5 nanometers toabout 50 nanometers. The height of the carbon nanotubes can be in arange from about 50 nanometers to about 5 millimeters.

Referring to FIG. 9 and FIG. 10, the carbon nanotube array 30 can bemade by the following steps:

(S30) providing a substrate 232 with a catalyst layer 230 on a surfaceof the substrate 232, and placing the substrate 232 into a reactiondevice 200;

(S31) supplying three kinds of carbon source gases, each of the carbonsource gases including different kinds of single carbon isotope;

(S32) introducing the three kinds of carbon source gases into thereaction device 200 simultaneously; and

(S33) controlling the different areas of the catalyst layer 230 toachieve different reaction temperatures to grow the carbon nanotubearray 30 on a surface of the catalyst layer 230.

In step (S30), the substrate 232 and the catalyst 230 are the same asthe substrate 132 and the catalyst 130, respectively. The reactiondevice 200 includes a reaction chamber 220, a reaction furnace 222 andtwo laser heating devices 240 for heating the reaction chamber 220 andthe catalyst layer 230, a protective gas supply conduit 202, threecarbon source gas supply pipes 204, 206, 208, and a vent-pipe 210. Theprotective gas supply conduit 202 is controlled by a valve 212. Thecarbon source gas supply pipe 204 is controlled by a valve 214. Thecarbon source gas supply pipe 206 is controlled by a valve 216. Thecarbon source gas supply pipe 208 is controlled by a valve 218.

The substrate 232 with the catalyst layer 230 is obliquely placed intothe reaction chamber 220 of the reaction device 200 such that thesubstrate 232 is obliquely oriented relative to the horizontal directionand the carbon source gases has less of a distance to reach thesubstrate 232. An angle between the substrate 232 and the horizontaldirection is about 45°, to improve the growth uniformity of the carbonnanotube array 30. When the substrate 232 with the catalyst layer 230 isplaced into the reaction chamber 220, the whole catalyst layer 230 canbe heated to a predetermined temperature. The two laser heating devices240 can irradiate the two partial areas of the catalyst layer 230 andallow the two partial areas of the catalyst layer 230 to achieve highertemperatures.

In step (S31) and step (S32), the three kinds of carbon source gases areprovided and introduced into the reaction chamber 220 simultaneously.The three kinds of carbon source gases are methane including a singlecarbon-14 isotope, ethylene including a single carbon-13 isotope, andacetylene including a single carbon-12 isotope.

In step (S33), the entire catalyst layer 230 is heated to a firsttemperature T₁ by the heating device (not shown) in the reaction furnace222. Meanwhile, a first reaction area of the surface of the catalystlayer 230 can be heated by a laser heating devices 240 until a secondtemperature T₂ is reached, and a second reaction area of the othersurface of catalyst layer 230 can be heated by another laser heatingdevice 240 until a third temperature T₃ is reached. The firsttemperature T₁ is in a range from about 600° C. to about 650° C., thesecond temperature T₂ is in a range from about 650° C. to about 800° C.,and the third temperature T₃ is in a range from about 850° C. to about1100° C. After a given time, the carbon nanotube array 30 is formed.

Because the second temperature T₂ reaches the decomposition temperatureof acetylene and ethylene, the acetylene including a single carbon-12isotope and the ethylene including a single carbon-13 isotope willdecompose together, to grow the second isotope-doped carbon nanotubesub-array 34 on the first reaction area of the catalyst layer 230. Thethird temperature T₃ reaches the decomposition temperature of methane,acetylene, and ethylene, therefore, the methane including a singlecarbon-14 isotope, the acetylene including a single carbon-12 isotope,and the ethylene including a single carbon-13 isotope will decomposetogether, to grow the third isotope-doped carbon nanotube sub-array 36on the second reaction area of the catalyst layer 230. Because the firsttemperature T₁ only reaches the decomposition temperature of acetylene,the acetylene including a single carbon-12 isotope will decomposeindividually, to grow the first isotope-doped carbon nanotube sub-array32 on the other areas of the catalyst layer 230.

Referring to FIG. 11, a carbon nanotube array 40 is disclosed. Thecarbon nanotube array 40 can be formed on a catalyst layer 230 of thesubstrate 232. The carbon nanotube array 40 includes a firstisotope-doped carbon nanotube sub-array 42, a second isotope-dopedcarbon nanotube sub-array 44 and a third isotope-doped carbon nanotubesub-array 46. Each isotope-doped carbon nanotube sub-array includes aplurality of carbon nanotubes. Each carbon nanotube in eachisotope-doped carbon nanotube sub-array is made up of a single carbonnanotube segment. The carbon nanotubes of the first isotope-doped carbonnanotube sub-array 42 are composed of carbon-12 isotope. The carbonnanotubes of the second isotope-doped carbon nanotube sub-array 44 arecomposed of carbon-12 isotope and carbon-13 isotope. The carbonnanotubes of the third isotope-doped carbon nanotube sub-array 46 arecomposed of carbon-12 isotope, carbon-13 isotope, and carbon-14 isotope.The carbon-12 isotope and carbon-13 isotope in the carbon nanotubes ofthe second isotope-doped carbon nanotube sub-array 44 are mixeduniformly at any proportion. The carbon-12 isotope, carbon-13 isotope,and carbon-14 isotope in the carbon nanotubes of third isotope-dopedcarbon nanotube sub-array 46 are also mixed uniformly in any proportion.

The first isotope-doped carbon nanotube sub-array 42, the secondisotope-doped carbon nanotube sub-array 44, and the third isotope-dopedcarbon nanotube sub-array 46 are located on the surface of thesubstrate, and spaced from each other. The first isotope-doped carbonnanotube sub-array 42, the second isotope-doped carbon nanotubesub-array 44, and the third isotope-doped carbon nanotube sub-array 46can have the same shape and size. Alternatively, depending on theapplication, the size of the isotope-doped carbon nanotube sub-array canbe different, and the shape of the isotope-doped carbon nanotubesub-array can be square, round, oval, rectangle, or other geometricshapes.

Referring to FIG. 12, the carbon nanotube array 40 can be made by thefollowing steps:

(S40) providing a substrate 232 with a catalyst layer 230 on a surfaceof the substrate 232, and placing the substrate 232 into a reactiondevice 200;

(S41) supplying three kinds of carbon source gases, wherein the carbonelement in each carbon source gas includes a single carbon isotope;

(S42) introducing the three kinds of carbon source gases into thereaction device 200 simultaneously; and

(S43) controlling the different areas of the catalyst layer 230 toachieve different reaction temperatures to grow the carbon nanotubearray 40 on a surface of the catalyst layer 230.

The step (S40), step (S41), and step (S42) are substantially the same asthe step (S30), step (S31), and step (S32), except that three laserheating devices 240 are provided for heating the reaction chamber 220and the catalyst layer 230. The three laser heating devices 240 canirradiate different areas of the surfaces of the substrate 232, and thelaser energy can pass through the substrate 232 and indirectly heat thecorresponding reaction areas of the catalyst layer 230 to achievedifferent temperatures. Heating the catalyst layer 230 indirectly canprevent the growth of carbon nanotubes from damage by the irradiation ofthe laser heating devices 240.

In step (S43), a first laser heating device 240 irradiates a first areaof the substrate 232, and the laser energy passes through the substrate232 and heats a corresponding first reaction area of the catalyst layer230 to achieve a first temperature T₁. Simultaneously, a second laserheating device 240 irradiates a second area of the substrate 232, andthe laser energy passes through the substrate 232 and heats acorresponding second reaction area of the catalyst layer 230 to achievea second temperature T₂. At the same time, a third laser heating device240 irradiates a third area of the substrate 232, and the laser energypasses through the substrate 232 and heats a corresponding thirdreaction area of the catalyst layer 230 to achieve a third temperatureT₃. The first temperature T₁ is in a range from about 600° C. to about650° C., the second temperature T₂ is in a range from about 650° C. toabout 800° C., and the third temperature T₃ is in a range from about850° C. to about 1100° C. After a given time, the carbon nanotube array40 is formed on the surface of the catalyst layer 230.

It is noted that because the first temperature T₁ only reaches thedecomposition temperature of acetylene, the acetylene including a singlecarbon-12 isotope will decompose by itself to grow the firstisotope-doped carbon nanotube sub-array 42 on the first reaction area ofthe catalyst layer 230. When the second temperature T₂ reaches thedecomposition temperature of acetylene and ethylene, the acetyleneincluding a single carbon-12 isotope and the ethylene including a singlecarbon-13 isotope will decompose together to grow the secondisotope-doped carbon nanotube sub-array 44 on the second reaction areaof the catalyst layer 230. When the third temperature T₃ reaches thedecomposition temperature of methane, acetylene, and ethylene, themethane including a single carbon-14 isotope, the acetylene including asingle carbon-12 isotope and the ethylene including a single carbon-13isotope will decompose together, to grow the third isotope-doped carbonnanotube sub-array 46 on the third reaction area of the catalyst layer230. Because the temperature of the other area of the catalyst layer 230is lower than the decomposition temperature of methane, acetylene, andethylene, there is no carbon source gas decomposed on other area of thecatalyst layer 230, and no carbon nanotubes formed on the other area ofthe catalyst layer 230.

Furthermore, the temperatures of the first, second, and third reactionarea of the catalyst layer 230 can be adjusted by the laser heatingdevice 240 to achieve different temperatures to grow carbon nanotubeswith a plurality of carbon nanotube segments in the carbon nanotubesub-array.

As described above, the isotope-doped carbon nanotube arrays include aplurality of isotope-doped carbon nanotube sub-arrays, and each of theisotope-doped carbon nanotube sub-arrays have a plurality ofisotope-doped carbon nanotubes composed of different kinds of carbonisotopes. Thus, the disclosure can provide a variety of isotope-dopedcarbon nanotubes at the same time. The variety of isotope-doped carbonnanotubes can be used to label a variety of unlabeled structures.

The method for making the isotope-doped carbon nanotube array has atleast the following advantages. First, various kinds of isotope-dopedcarbon nanotubes having various kinds of carbon nanotube segments can beprepared easily by controlling the reaction temperature of differentcarbon hydrogen compounds. Second, by controlling the different reactiontemperature of different areas in the catalyst layer, and reacting thecarbon source gases on different areas under different temperatures, aplurality of isotope-doped carbon nanotube sub-array can be prepared atthe same time, thereby reducing the preparation time. Furthermore, thereaction mechanism of carbon hydrogen compounds to prepare carbonnanotubes can be further studied.

It is to be understood the above-described embodiment is intended toillustrate rather than limit the disclosure. Variations may be made tothe embodiment without departing from the spirit of the disclosure asclaimed. The above-described embodiments are intended to illustrate thescope of the disclosure and not restricted to the scope of thedisclosure.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A method for forming a carbon nanotube array, themethod comprising steps of: (a) providing a substrate with a catalystlayer on the substrate, and placing the substrate into a reactionchamber; (b) supplying at least two kinds of carbon source gases, eachcarbon source gas comprising a single carbon isotope, wherein the carbonisotopes of the at least two kinds of carbon source gases are differentfrom each other; (c) introducing the at least two kinds of carbon sourcegases into the reaction chamber of the reaction device simultaneously;and (d) heating the whole catalyst layer to a first temperature to reactone of the carbon source gases under the first temperature, andsimultaneously controlling at least one part area of the catalyst layerto a second temperature higher than the first temperature, whereby asecond isotope-doped carbon nanotube sub-array is formed on the at leastone part area, and a first isotope-doped carbon nanotube sub-array isformed on other areas of the catalyst layer other than the at least onepart area, the second isotope-doped carbon nanotube sub-array beingcomposed of at least two kinds of carbon isotopes.
 2. The method ofclaim 1, wherein the catalyst layer is selected from the groupconsisting of iron, copper, cobalt, nickel, and any alloy thereof. 3.The method of claim 1, wherein the at least two kinds of carbon sourcegases are hydrocarbons.
 4. The method of claim 3, wherein thehydrocarbons are selected from the group consisting of methane,acetylene, ethylene, and allene.
 5. The method of claim 1, wherein thestep (b) further comprising steps of: evacuating the reaction chamber;and introducing a protective gas into the reaction chamber.
 6. Themethod of claim 5, wherein the protective gas is selected from the groupconsisting of argon, nitrogen, helium, and neon.
 7. The method of claim1, wherein the first temperature and the second temperature aredecomposition temperatures of the at least two carbon source gases. 8.The method of claim 1, wherein the temperatures of the different areason the catalyst layer are controlled by at least one laser heatingdevice.
 9. The method of claim 1, wherein the substrate with thecatalyst layer is obliquely placed into the reaction chamber such thatthe substrate is obliquely oriented relative to the horizontaldirection.
 10. The method of claim 1, wherein an angle between thesubstrate and the horizontal direction is about 45°.
 11. The method ofclaim 1, wherein the at least two kinds of carbon source gases comprisethree kinds of carbon source gases, and the step (d) further comprises astep of: simultaneously controlling at least one second part area of thecatalyst layer to a third temperature higher than the secondtemperature.
 12. The method of claim 1, wherein the at least two kindsof carbon source gases comprise three kinds of carbon source gases, andfurther comprising step: (e) heating the whole catalyst layer to thesecond temperature, and simultaneously controlling the at least one partarea of the catalyst layer to a third temperature higher than the secondtemperature.